68 
IOWA ACADEMY OF SCIENCE 
Explanation op Plate IV, 
Fig. 1. A portion of the face of the loess bluffs at Council Bluffs, Iowa, showing 
the tufted xerophytic vegetation with large bare spaces between the plants. 
Dust may therefore be whipped up these abrupt slopes much as snow is 
driven up the face of a snow-drift. (See p. 58.) 
Fig. 2. A view of the top of the high ridge above Hamburg, Iowa, looking north. 
The slopes to the left face the river and are treeless. The eastern 
sheltered side is forest-covered and less abrupt. Where the eastern slopes 
of these ridges are treeless the return currents of air also whip the dust 
toward the crest of the ridge, and make these slopes almost as abrupt 
as those on the west side. (See p. 58.) 
